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5F6A Hum...

Discussion in 'Amp Tech Center' started by MrCoolGuy, Aug 25, 2020.

  1. andrewRneumann

    andrewRneumann Tele-Holic

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    That sounds odd. Inrush current from multiple ON OFF cycles? Maybe time to upgrade to 1W metal oxide.
     
  2. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Sorry, I guess mentioning that might have saved a hundred or so posts!
     
  3. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Yeah... it has a 1 watt metal film. Most things do in this amp. But maybe I should bump it up.
     
  4. andrewRneumann

    andrewRneumann Tele-Holic

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    You would think that 1W would be enough.

    Mr. Aiken says:
    Q:What kind of resistors do you recommend for power supply decoupling use?
    A: I recommend 5W (or a higher power rating if needed) 1% 750V metal oxide resistors for this application. They have higher surge/overload capability than the film types, excellent long-term stability, and flameproof construction. Note that lower-power metal oxides, such as 1W and 2W are usually only rated for 350V and should be avoided for this application. Even though the voltage across the resistor in normal operation is only 50 volts or so, it can be much higher at turn on, or if a tube fails. Another good type to use is the Ohmite OX/OY series ceramic composition resistors. These don't have the tight temperature coefficient or tolerance (typically 10%) that metal oxides do, but they are designed for heavy surge use.

     
  5. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Interesting... i never thought those ceramic resistors would be necessary is a vintage style amp. But hey...
     
  6. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Thanks for that!

    So the hiss isn't bad. Especially since I put better tubes in and biased. (I had taken out my good ones while we were doing all that work)
     
    D'tar likes this.
  7. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    @D'tar
    So the presence control is better this way. More usable with the pot turned down than before. I'm going to do my balanced bias pots next... for some old tubes I have. But after that, I may hit you up regarding nfb/presence.
     
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